1. Field of the Invention
The present invention relates to an apparatus for controlling the tension of a running print sheet or web for use with a rotary press.
2. Description of the Related Art
A typical monochromatic perfecting unit and of a typical monochromatic perfecting and multicolor oneside printing unit for use with a conventional rotary press are shown in FIG. 1 and FIG. 2, respectively. According to the monochromatic perfecting unit as shown in FIG. 1, a running printing sheet or web of paper 1 is, after having been printed by the monochromatic perfecting unit 2, directed through a guide roller 3 toward a midway drag roller 4, whereby the web of paper is subjected to traction to be delivered to following operations.
According to the monochromatic perfecting unit and the multicolor one side printing unit as typically shown in FIG. 2, the running web 1 is, after having been printed by the monochromatic perfecting unit 2, directed through a guide roller 5 toward a midway drag roller 4, whereby the web is subjected to traction to be delivered to a multicolor one side printing unit 5, where the web is subjected to the multicolor printing operations and is then redirected to following procedures in the printing line.
In the construction of the rotary press as schematically shown in FIGS. 1 and 2, it is observed that there occurs a substantial variation in tension of the running web 1 extending in the upstream and downstream of the monochromatic perfecting unit 2 and the multicolor one-side printing unit 5. This variation in tension of the web is considered to result from the possible loss of tension by way of the slots of the printing cylinder and of vibrations occurring per one operating cycle of the printing cylinder, and such variations in tension result in such faults such as deviations in the cutting of the printings and such as offset doubles, or the like.